1. Field of the Invention
The present invention relates to a method for making an implantable pacing lead tip electrode for use with a pacing lead assembly. The tip electrode is formed from an electrically conductive material and with a plurality of grooves or recesses which are etched into the tip electrode circumferentially and parallel to the horizontal and vertical transverse axes of the tip electrode to provide a large surface area within a small displaced surface area on the tip electrode to minimize electrode polarization while providing sufficient current flow for heart muscle depolarization.
2. Description of the Prior Art
Heretofore, various tip electrodes have been proposed having porous surfaces or other surfaces for increasing the surface area of the tip electrode. Examples of such previously proposed electrodes are disclosed in various prior U.S. patents.
For example, the Enger U.S. Pat. No. 4,011,861 discloses an implantable electric terminal for organic tissue which is porous and intermeshes with the tissue. The electric terminal is composed of a tissue-compatible implantable material which is electrically conductive, such as platinum or an alloy, and which has on at least one surface thereof a porous material or layer having pores that are interconnected and continuous so that body electrolytes and/or tissue containing blood capillaries can contact the electrically conductive material through the porous material or layer.
The MacGregor U.S. Pat. No. 4,280,514 discloses an endocardial pacemaker electrode having a dense rigid metal substrate and a rigid porous metal coating which adheres to at least a major portion of the substrate. The porous coating includes a plurality of metal particles bonded together at their points of contact with each other and with the substrate to form a network of interconnected pores substantially uniformly distributed throughout the coating.
The King U.S. Pat. No. 4,352,360 discloses a semi-conductor low-threshold electrode having a plurality of materials which are arranged in layers such that the material having the lowest conductivity is in direct contact with body tissue.
The Hirshorn et al U.S. Pat. No. 4,407,302 discloses a cardiac pacemaker electrode tip structure having an electrode tip having an external surface with a concave region formed thereon to increase the pacing impedance thereof. The external surface of the electrode tip is roughened to increase the microsurface area of the electrode tip and to reduce the sensing impedance thereof.
The Hirshorn et al U.S. Pat. No. 4,408,604 discloses a porous pacemaker electrode tip comprising a concavo-convex electrode cap having a plurality of apertures therethrough and an electrode shaft having a supporting edge formed thereon to which the concave surface of the electrode is joined. The porous cardiac pacemaker electrode is formed by deforming a platinum plate into a concave-convex shaped cap member, thereby forming a plurality of selectively spaced apertures through the electrode cap member to make the electrode cap substantially porous.
The Bussard et al U.S. Pat. No. 4,440,178 discloses an implantable electrode which is porous and includes a sintered member made of electrically conductive particles. The particles are covered with a material of lower electrical conductivity than that of the particles, the particles being metals selected from the group comprising tantalum, titanium, molybdenum, zirconium or cobalt-chromium based alloys.
As will be described in greater detail hereinafter, the tip electrode and the method of making same of the present invention differ from the various tip electrodes previously proposed by providing a tip electrode having a plurality of grooves etched into the surface of the tip electrode to provide a large surface area to minimize polarization of the electrode while at the same time, keeping the same overall outer diameter of the electrode so that the large surface area is within a small displaced surface area to ensure an electric current flow sufficient to cause muscle depolarization of the heart. Since the grooves are etched into the surface of the tip electrode, the pattern of and the number of grooves can be controlled and can be easily changed.